The blast occurred in Cairo's Abbassyia district early Sunday morning, Egypt’s health ministry said.
Security forces are searching and screening the area, CNN reported.
It remains unclear what caused the blast near Saint Mark's Coptic Orthodox Cathedral.
The explosion comes just two days after two bombs killed six police officers and a civilian in Giza's Haram district on the street leading to the pyramids.
Copts have faced persecution and discrimination that spiked after the toppling of Hosni Mubarak's regime in 2011. Dozens have been killed in sectarian clashes. There is also little Christian representation in government.
Coptic Christians make up about 10 percent of Egypt's 80 million residents, according to the CIA's World Factbook They base their theology on the teachings of the Apostle Mark, who introduced Christianity to Egypt, according to St. Takla Church in Alexandria, the capital of Coptic Christianity.